How is goserelin (GnRH agonist) administered?

Administration of Goserelin

Goserelin is administered as a subcutaneous depot injection, typically 3.6 mg every 28 days (4 weeks) into the upper abdominal wall. 1

Formulation and Delivery Method

Goserelin is supplied as a sterile and biodegradable D,L-lactic and glycolic acids copolymer implant containing 3.6 mg of goserelin in a disposable syringe device with a 16-gauge needle and protective sleeve 1. The implant is designed as a depot formulation that releases the medication continuously over a 28-day period at an average rate of approximately 120 micrograms/day 2.

Administration Procedure:

• The injection is given subcutaneously into the upper abdominal wall
• Local anesthetic may be required for some patients before injection 3
• The biodegradable implant dissolves over time and does not need to be removed

Dosing Options

Standard Dosing:

• 3.6 mg subcutaneous depot injection every 28 days (4 weeks) 1, 4
• 10.8 mg subcutaneous depot injection every 12 weeks (3 months) is also available 5

Clinical Applications and Dosing:

1. Prostate Cancer:

   • Standard dose: 3.6 mg subcutaneously every 28 days 4
   • May be used as monotherapy or in combination with radiation therapy 4
   • When used with radiation therapy, goserelin is typically started on the first day of radiation or up to 2 months before radiation 4

2. Breast Cancer:

   • Standard dose: 3.6 mg subcutaneously every 28 days 1
   • In premenopausal women with hormone-responsive breast cancer, goserelin is often combined with tamoxifen or aromatase inhibitors 6
   • Duration typically ranges from 2-5 years, with 5 years being optimal 6

3. Fertility Preservation:

   • Used in young women undergoing chemotherapy for breast cancer to protect ovarian function 4
   • Started before initiation of chemotherapy and continued concurrently 4

Pharmacokinetics and Mechanism

After administration, goserelin initially causes a transient increase in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels, followed by downregulation of receptors in the pituitary gland 4. This leads to:

• Suppression of serum LH and FSH to follicular phase levels within 4 weeks 1
• Reduction of testosterone to castrate levels in men within 3-4 weeks 4
• Suppression of estradiol to postmenopausal levels in women 1

The pharmacokinetic profile shows:

• Peak plasma concentration occurs between 8-22 days in females and 12-15 days in males 1
• Slower release during the first 8 days, followed by more rapid and continuous release for the remainder of the 28-day period 1

Common Pitfalls and Considerations

1. Initial Flare Phenomenon:

   • During the first 1-2 weeks of treatment, there is a transient rise in hormone levels that may worsen symptoms in patients with advanced disease 4
   • In prostate cancer, this may be managed by adding an antiandrogen during the initial treatment period 4

2. Monitoring Requirements:

   • In premenopausal women receiving goserelin with aromatase inhibitors, estradiol levels should be monitored to confirm adequate ovarian suppression 6
   • In approximately 5% of women, FSH and LH levels may not be adequately suppressed 1

3. Return to Baseline:

   • Hormone levels typically return to pretreatment values within 12 weeks after the last implant administration 1

By understanding the proper administration technique and dosing schedule, clinicians can effectively use goserelin to achieve the desired hormonal suppression for various clinical indications while minimizing potential complications.